Fault detection apparatus

ABSTRACT

Fault detection apparatus for use with an electric control circuit for a machine tool or other instrumentality having a plurality of devices each of which must function in a predetermined manner to establish a predetermined circuit condition, the apparatus having means operable in response to faulty operation of any of such devices to indicate specifically which of such devices is faulty.

United States Patent [191 Scourtes 1 1 Apr. 10, 1973 54] FAULT DETECTIONAPPARATUS 3,611,340 10/1971 Harte et al .,...340 256 x 3,505,664 4 1970Morris ..340/256 [75] Inventor- Gem'ge Dem), 2,719,966 10/1955 Schurr..340 415 [73] Assignee: Wilson Engineering, Inc., Saginaw,

' Mi h Primary Examiner.l0hn W. Caldwell Assistant Examiner-Daniel Myer[22] Filed: Dec. 17, 1969 An0mey Learman & Mccuuoch [21] A 1.No.: 885897 pp 57 ABSTRACT 52 vs. C] ..340/256, 340/253 c, 340/415. Faultdetection apparatus for use with an electric 51 Int. Cl. ..G08b 21/00,G08b 23/00 circuit a machine Or other instrumentality [58] Field 61Search ..340/253 213 415 having a plurality 0f devices each which mustfunc- 6 tion in a predetermined manner to establish a predeterminedcircuit condition, the apparatus having means operable in response tofaulty operation of any [56] References Cited of such devices toindicate specifically which of such UNITED STATES PATENTS devices is y-2,599,623 6/1952 Forrester ..340 213 R x 4 Claims, 2 Drawing Figures {0{G 10 [O -v- I 3| 32 33 I 31 32 33 I 31 32 33 I 3 32 33 }-2 27 L. E 27 0E 27- 2 a 27 2 E 1 1 J r b D/ 27 27 27 27 25 -26 25 "-26 25 T-"ZG 25 -2sT Q as T as T ,128 26 E1 I s 'H: W" V 1% um/W FAULT DETECTION APPARATUSThis invention relates to fault detection apparatus for an electriccontrol circuit of a machine tool or the like, the circuit having aplurality of current or voltage regulating devices which must functionin a predetermined manner to produce a desired circuit condition, andmore particularly to apparatus for indicating the malfunction of any oneof such devices.

In recent years, control systems for various types of machinery havebeen developed which are elaborate and extremely complex. Such systemscommonly employ a multitude of switching and relay devices which areoperated singly and in combination. When a fault occurs in one of theelements in such systems, much time is lost in attempting to isolate andidentify the particular element which is malfunctioning. There are noknown fault detection devices by means of which a particular one of alarge number of elements has been rendered inoperative.

Detection apparatus of the type referred .to herein may be employed inconnection with one or more machine tools which have their own automaticcontrol systems and do not require constant operator surveillance, butare monitored remotely by means of a computer to which signals are fedfrom the operating machine. When one or more of the elements in themachine s control system malfunctions, the fault detection apparatusaccording to the present invention provides a positive indication of thespecific, malfunctioning elements.

According to the present invention, there is provided fault detectionapparatus for use in detecting a fault in a control circuit which isadapted to be connected to a source of electrical energy for supplyingan electrically operable device with a normal operating signal. Such adevice may comprise a relay having a minimum threshold operating signallevel and a normal operating signal level. When a fault occurs in thecontrol circuit, the fault indicating means continues to provide asignal to the electrically operable device, but at a level below theminimum threshold level.

With the foregoing in view, the present invention consists of thecombination and arrangement of parts, hereinafter more fully described,illustrated in the accompanying drawings and more particularly pointedout in the appended claims, it being understood that changes may be madein the form, size, proportion and details of construction withoutdeparting from the spirit or sacrificing any of the advantages of theinvention.

In the drawings:

FIG. 1 is a block diagram illustrating a typical system which includesfault'detection apparatus according to the invention; and

FIG. 2 is an electrical diagram illustrating a typical fault detectioncircuit according to the invention.

A tooling machine which may be utilized to perform one or moreoperations on a work piece is shown at block receiving control signals11 from a control circuit designated generally by the block 12. Outputsignals from the control circuit 12 may be responsive to a plurality ofconditions such as time, location of the workpiece, and the availabilityof power. If a malfunction occurs in one or more of the operatingelements in the control circuit 12, a signal is provided at 14 to anelectrically operable indicating means 15. Where, as is the usual case,a large number of elements are provided in the control circuit 12, acomputer, which may comprise a commercially available digital computer,is shown at block 13 for monitoring the operability of the controlcircuit 12. The proper time-phase operating sequence of all elements inthe machine tool control circuit is programmed into the computer memory.If the tooling machine 10 fails to operate properly, the computer 13interrogates each element in the control circuit 12 and compares itsoperating condition with the programmed condition to rapidly provide anindication of which of the elements are malfunctioning.

FIG. 2 discloses a portion of the machine tool control circuit 12 inbroken lines at 12' and includes a control device such as a relay Rconnected across power lines L, and L through a plurality of switchingdevices S and S.,. The lines L, and L may be connected across a sourceof power such as 110 volt, cycle alternating current. The devices S, S,may comprise one or more limit switches such as those shown at S, and8,, one or more relay operated switches such as that shown at 8,, one ormore timer controlled switches suh as that shown at S,,, or anycombination thereof. The relay operated switch S is controlled by thecoil 17 having terminals L, and L connected with an energizing source ofcurrent, not shown. The timer for the switch S is shown at 16. Thecontrol relay R may be of the type having a normal operating current,such as milli-amperes, and a minimum threshold current, such as 60milli-amperes, required to close its normally open contacts R, and openthe normally closed contacts R, which are connected in series circuitwith solenoids 20 and 21, respectively, across the lines L, and L Thesolenoids 20 and 21 may be connected to control valves for pressurefluid cylinders (not shown), a chuck (not shown), or the work piece (notshown) to be machined to initiate or cease a particular operation of themachine tool. It will be understood that these examples are notexhaustive but'merely illustrative of the operations which may becontrolled by the relay R and the solenoids 20 and 21.

When the devices S, S, are in their closed condition simultaneously,current will flow from line L, to line L, to energize the relay R withthe normal operating current of 100 milli-amperes and thereby establisha predetermined circuit condition. Thus, the devices S, S, control thesupply of operating current to the relay R, and all of these devicesmust be closed to enable operating current to be delivered to the relay.

Fault detecting means D is associated with the control circuit 12 fordetecting and indicating malfunctioning of any of the devices S, S, andcomprises a plurality of voltage step down transformers T, correspondingin number to the number of devices S, coupled to the associated deviceS. The transformers are connected in parallel with the devices S, S, bymeans of conductors 37 40. The output of each transformer is convertedto a DC signal by sets of diodes 25 and 26 wich are connected acrosseach of the secondary windings 28, and a return wire 27 is connected tothe midtap of each of the secondary windings through a limiting resistor27'. The voltage is stepped down to provide a low level DC monitoringvoltage which is limited to a specific value depending upon theparticular value of a Zener diode 32 which is connected across theoutput of each secondary winding 28. A ripple filter capacitor 31isconnected across the diode 32 to provide a steady state DC voltage. Anindicator, such as a lamp 33, is connected across each Zener diode 32and is operable to glow in response to a signal across the secondary ofthe as sociated transformer. Aural signals may be used in lieu of lamps,if desired. Terminals a and b may be connected to the monitoringcomputer 13.

The construction and arrangement of the apparatus described thus far aresuch that, when all of the switch devices S, S, are closed, thetransformers T are shunted, normal operating current is supplied to therelay R to energize the latter, and the detecting apparatus is inactive.Should one or more of the devices S, S, be open circuited, however, thetransformer associated therewith will be energized, the associatedindicating lamp 33 will be illuminated, an appropriate signal will betransmitted from the terminals a, b to the computer, and the currentsupplied tothe relay R will be less than that required to energize it.

In operation, the switching devices S, S, will be moved to their closedposition in any suitable manner so as to establish a circuit conditin inwhich the relay R is connected across the lines L, and L With the switchdevices S, S, in the closed position, the primary windings 24 of thetransformers T will be shunted and no signal will be detected across theoutput of the transformer secondary windings 28. The lamps 33,therefore, will be dark. As the current to the relay R builds to thethreshold value, such as 60 milli-amperes, the relay R is energized,thereby closing the normally open contacts R, to energize the solenoidand opening the normally closed contacts R, to interrupt current flow tothe solenoid 21. The valves or other devices controlled by suchsolenoids will operate in a predetermined manner.

Assuming that a fault occurs in one of the switch devices, such as anopen circuit in the device 8,, cur

rent will flow from the line L, through the switch 8,, the

conductor 37, the primary winding 24 of the transformer T the conductor38, the switches S and 5,, and the relay R to the line L,,. Theimpedance of the primary windings 24 is so selected that when currentflows through one of the primary windings, current will continue to besupplied to the relay R, but at a value lessthan the 60 milli-amperesnecessary to maintain the relay energized. Consequently, the relay willbe deenergized, thereby closing the contact R, and opening the contactsR The voltage appearing across the primary winding 24 of the transformerT will be stepped down through the secondary winding 28 and rectifiedthrough the diodes 25 and 26 connected thereacross and then deliveredvia the lamp 33 to the monitoring computer.

In the foregoing example, the lamp 33 associated with the switch S, willbe the only illuminated lamp in the detector circuit. lndicia may beplaced adjacent this lamp to indicate to the operator that it is theswitch S, which is faulty. In this manner it is unnecessary that acontinuity check of each individual element in the entire circuit betested in order to determine which element or elements has or have beenrendered inoperative. The bank of lamps 33 may be mounted on a controlpanel which is readily accessible to an operator.

If a plurality of the switch devices S is rendered inoperative, thelamps associated with the individual switches will glow. To illustrate,assume that the switch device 5,, as well as the switch S is opencircuited. Current will flow to the relay R through the switch 8,, theline 37, the primary winding 24 of the transformer T the line 38, theswitch S5, the conductor 39, the primary winding 24 of the transformer Tand the conductor 40. Thus, the indicator lamps 33 associated with thetransformers T and T, will light simultaneously, thereby indicating tothe operator that two devices S and S, are faulty. The current throughthe relay R will again be insufficient to maintain the latter energized.

The circuit will also operate to detect and indicate a short-circuit inone of the switches S, and S.,. If, for example, the switches S S, arein the closed position and the switch S, is in the open position forproper circuit operation, the lamp 33 associated with the switch S, willilluminate and a signal, i.e., 5 volts, will be detected across theterminals a and b. To determine proper circuit operation, the operatormay visually check the lamp and compare its time of illumination with atime phase sequence chart at the disposal of the operator or the 5 voltsignal at terminalsa and b may be detected by the computer 13, andcompared with the stored information in the computer memory as to theproper voltage for this particular time. If the switch S, shouldshort-circuit, the lamp 33 associated therewith would fail to operate,thus providing an indication that the switch 5, is inoperative. Therewould be no signal across the terminals a and b at this time, thus, thecomputer 13 would detect and comparethe absence of the signal with thestored information as to the proper signal and provide an indication ofthe malfunction in the normal manner.

The disclosed embodiment is representative of the presently preferredform of the invention, but is intended to be illustrative rather thandefinitive thereof.

lclaim:

1. Fault detection and monitoring apparatus for use with an electriccircuit which controls the operation of an instrumentality and includesa plurality of electrically operable devices which are operable inelectrical current conducting and non-conducting conditions and mustoperate in a predetermined manner to establish a predetermined circuitcondition, said devices being adapted to be connected with a source ofelectric alternating current power, said apparatus comprising:.

electrically operable detecting means for detecting the condition ofsaid devicesincluding an input circuit coupled to each of said devicesand said source of electric power and an output circuit providing acontinuous electrical output signal when any one of said devices is insaid nonconducting condition; and I monitoring means responsive to thecontinuous electrical output signal of said detecting means forcomparing the value of said continuous signal with a predetermined valueand indicating whether said devices are operating in said predeterminedmanner; I said detecting-means comprising:

transformer means, having primary winding means and secondary windingmeans for coupling said electrically operable devices and said source ofpower to said monitoring means, said primary winding means being adaptedto be connected to said source of power and connected in parallelcircuit relation with said devices; and rectifier circuit meansconnected to said secondary winding means to rectify the signal coupledto said secondary winding means and provide said continuous signal;saidmonitoring means being connected to said rectifier circuit means tobe energized by said continuous signal.

2. Fault indicating apparatus as set forth in claim 1 including anelectric circuit element connected in circuit with said electricallyoperable devices; said element being operable in response to a minimumthreshold current level, said coupling means being rectifier circuitmeans for limiting said continuous signal to a predetermined value.

1. Fault detection and monitoring apparatus for use with an electriccircuit which controls the operation of an instrumentality and includesa plurality of electrically operable devices which are operable inelectrical current conducting and non-conducting conditions and mustoperate in a predetermined manner to establish a predetermined circuitcondition, said devices being adapted to be connected with a source ofelectric alternating current power, said apparatus comprising:electrically operable detecting means for detecting the condition ofsaid devices including an input circuit coupled to each of said devicesand said source of electric power and an output circuit providing acontinuous electrical output signal when any one of said devices is insaid non-conducting condition; and monitoring means responsive to thecontinuous electrical output signal of said detecting means forcomparing the value of said continuous signal with a predetermined valueand indicating whether said devices are operating in said predeterminedmanner; said detecting means comprising: transformer means, havingprimary winding means and secondary winding means for coupling saidelectrically operable devices and said source of power to saidmonitoring means, said primary winding means being adapted to beconnected to said source of power and connected in parallel circuitrelation with said devices; and rectifier circuit means connected tosaid secondary winding means to rectify the signal coupled to saidsecondary winding means and provide said continuous signal; saidmonitoring means being connected to said rectifier circuit means to beenergized by said continuous signal.
 2. Fault indicating apparatus asset forth in claim 1 including an electric circuit element connected incircuit with said electrically operable devices; said element beingoperable in response to a minimum threshold current level, said couplingmeans being operable to provide continuous, limited current from saidsource to said element below said threshold level when a malfunctionoccurs to open circuit any one of said electrically operable devices. 3.Fault detection and monitoring apparatus as set forth in claim 1including means connected to said rectifier circuit means for limitingthe value of said continuous signal.
 4. Fault detection and monitoringapparatus as set forth in claim 1 including means connected to saidrectifier circuit means for limiting said continuous signal to apredetermined value.